1. Field of the Invention
The present invention relates to an image display device and a manufacturing method therefor. In particular, the present invention relates to an image display device in which an aperture ratio of a pixel may be improved and a manufacturing method therefor.
2. Description of the Related Art
A conventional liquid crystal display device includes a non-emissive type liquid crystal display panel and a backlight unit, which illuminates the liquid crystal display panel from a rear surface side thereof. In the liquid crystal display panel, thin film transistors are formed in respective pixels. In each of the pixels, which are formed in matrix in a display region, there are provided a storage capacitor for storing display data (video signal) for one frame period and a thin film transistor for controlling writing of the video signal to the storage capacitor. In the liquid crystal display panel formed as described above, a gate line is connected to a gate electrode of the thin film transistor, and a video signal line (drain line), to which the video signal is input, is connected to a drain electrode thereof. The video signal supplied from the drain line is read based on an on-signal from the gate line, and the video signal is stored in the storage capacitor.
However, in the conventional liquid crystal display device, it is known that, even when the thin film transistor is OFF, electric charges leak from the storage capacitor due to a backlight beam from the backlight unit. As a method of reducing influence on image display due to this leakage current, increasing the size of the storage capacitor is performed. Meanwhile, because there is a demand for high image quality and high definition in recent years, an area occupied for one pixel tends to be reduced. In accordance with this reduction in pixel area, the storage capacitance is reduced, and hence there is a demand for reduction in leakage current in the thin film transistor.
As a technology of reducing an off current, that is, a leakage current of the thin film transistor, for example, there is a technology described in Japanese Patent Application Laid-open No. 2004-193248. In this technology, a bottom gate type thin film transistor includes an interlayer insulating film between a gate electrode and a source/drain electrode. The interlayer insulating film has a groove formed therein in a channel region, and a polysilicon layer, which becomes a semiconductor layer, is formed in contact with a gate insulating film, the interlayer insulating film, a heavily doped semiconductor layer, and the source/drain electrode. In this technology, the semiconductor layer formed on the side surface portion of the interlayer insulating film plays a role as an offset, and hence, due to electric field relaxation at a drain end, the off current, that is, the leakage current is reduced.
In the technology described in Japanese Patent Application Laid-open No. 2004-193248, the semiconductor layer is formed so as to be located on the inside of the gate electrode, and the gate electrode blocks the backlight beam from directly entering the semiconductor layer. In this manner, it is possible to reduce a photoleakage current, which is a leakage current generated when the backlight beam is applied to the thin film transistor. However, when considering fluctuations in processing dimension of the gate electrode and the semiconductor layer, the gate electrode is required to be formed larger in width than the semiconductor layer. In this case, there is a fear of reduction in aperture ratio of a pixel.
In particular, in a liquid crystal display device mounted in a mobile terminal, there is a demand for high definition within a limited casing size, and hence the size of one pixel is reduced. Meanwhile, the size of the thin film transistor or the like within the pixel is limited by the processing accuracy and the drive ability thereof, and hence there is a demand for a thin film transistor having a smaller occupied area.